Why does my lime tree drop its fruit early?

Question

I have a kumquat and a Mexican (or Key) lime tree in pots right next to each other. The kumquat has been flowing and fruiting like a champ nearly as long as I've owned it. The lime hasn't yet produced a mature fruit. It has flowered many times and produced little fruit the size of a lime seed. But every time each fruit falls off the branches a few days later. Both trees are on the same watering and feeding schedule, get nearly the same sun, and are subject to the same weather.

Some (possibly crackpot) theories:

• Recent weather changes in Southern California are spooking the lime. (We've had hot days followed shortly by cold days. I never know if I should take a light jacket to work or not.)

• The lime just isn't happy with the climate. I gather they like lots of heat.

• The flowers aren't getting pollinated or are pollinated from a "bad" tree. I've seen bees working over the flowers, but I don't know if my neighbors have limes. To be safe, I self-pollinated the tree once, but no joy.

• I ought to increase the watering schedule when the fruit starts to grow. Both trees are one a strict once-a-week schedule.

• I'm over fertilizing the lime, which is quite a bit smaller (as it's younger) than the kumquat at this point.

• Critters and birds are vandalizing my lime.

• I just got a bum lime tree.

Are any of these theories likely to be the source of my problem?

(This question is about these trees for what it's worth.)

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I haven't had a chance to take photos, so here are the other requested details:

The kumquat is 2+ years old and I bought the lime 1/2 a year ago. I haven't pruned either tree. Both are roughly 2 feet tall, but the kumquat is sprawling out several feet on two sides while the lime looks like Charlie Brown's Christmas tree. The dimensions of the pot are:

Outside diameter: 15"
Max. diameter inner pot: 12 ½"
Height: 12 ½"
Inside diameter: 13 ¾"

(I don't at all know what "Max. diameter inner pot" means.)

Answer 1

According to Peggy A. Mauk, Ph.D. and Tom Shea:

This is frequently referred to as “June drop”. Young fruit (smaller than 1 inch in diameter) may drop in May, June and/or July. Some fruit drop is natural. Excessive drop may be due to drought stress, sudden high temperatures, low humidity, or nitrogen deficiency. Heavy pruning, thrips, mites, or spray injury can also cause fruit to drop. Keep trees in good health and well irrigated to minimize fruit drop. Fruit drop is a self-regulating mechanism in citrus trees.—"Questions and Answers to Citrus Management" [PDF]

The factors I noticed in the question that contributed to the problem were likely:

• "drought stress" (I manage my tree's water supply and was likely too stingy during the weeks leading up to and following fruiting.)
• "sudden high temperatures", and
• "low humidity".

This year, we've had a milder summer and I've tried to water more often during the warmer, dried periods. As a result, I have a small batch of limes that are growing and maturing. Citrus trees need moist soil for a good harvest. When the top few inches dry out, I add another bucket of water.

It's also possible there was a lack of nitrogen while the fertilizer spikes I use dissolved.

Answer 2

• Have you checked the pH of the soil AND water? Should be just right at 7...

• Are you using a citrus fertilizer? Should be using a fertilizer for citrus...

• Have you checked closely for pests? Some pests will feed on roots and you won't see them...

• Are you sure you're not OVER watering or feeding? That's a quick way to kill a plant slowly...

• Is the soil draining properly?

Lay off the watering on your lime by a week or more.. Let the plant wilt a bit before watering it again. Don't fertilize every week either, you may be causing salt buildup unless you're using organic, even then I'd only feed maybe twice a month!

Check that pH! Plant won't take nutrients if soil or water pH is too high or low and won't be able to hold fruit as a result..

Answer 3

Key lime trees by nature look like a 'Charlie Brown' tree. Kumquats are a fuller, more graceful tree. It could be your tree is still too young to set fruit. Even when it does, it will be a smallish size compared to a Bearss lime; smaller than a walnut.